In [1]}, Zontak et al. found that some patches exist only in a specific image and can not be found in any external database of examples. Therefore, SR methods trained on external images can not work well on such images due to the lack of patches information, while methods based on internal statistics may have a good performance. Meanwhile, Zontak et al. pointed out that the internal entropy of patches inside a single image was much smaller than the external entropy of patches in a general collection of natural images. Therefore, using the internal image statistics to further improve model performance is a good choice.
